Concrete Shrinkage Effect on Columns Strengthened with Concrete Jackets

Placing reinforced concrete (RC) jackets around RC columns is a common strengthening technique, particularly in seismic regions. The influence of concrete shrinkage on columns strengthened with a RC jacket has not been investigated yet. This paper presents an analytical procedure to calculate the stresses induced by shrinkage of the new concrete. A variable modulus of elasticity with time and relaxation due to creep are taken into consideration in the procedure. Finite element analysis method is used to perform parametric numerical simulations. From the results, it is found that jacket concrete shrinkage reduces the strength of composite columns. This strength reduction increases as the shrinkage strain values increase. For example, a value as low as 0,6 of monolithic behaviour was found for a normalised axial load of 0,4 and a concrete free shrinkage strain of 1600 microstrains. It is concluded that the effect of concrete shrinkage must be considered when strengthening RC columns, as it induces slip at the interface between the old and the new concrete and tensile stresses in the jacket concrete.